Lung cancer is a leading cause of cancer death. In the smoking population, mortality due to lung cancer has now surpassed that due to cardiovascular complications to become the largest killer. Bombesin is one of the major autocrine growth factors produced by small cell lung cancer (SCLC) cells. BB receptor antagonists and BB receptor antibodies, currently in clinical trials, prevent BB binding to its receptor resulting in blocking of BB action and inhibition of proliferation. We propose to study the BB receptor in NCI-H345, a SCLC cell line. stimulation of BB receptors in several tissues, including SCLC cells, leads to activation of phospholipase C and the generation of several inositol phosphate isomers. Our study will specifically focus on the generation of cyclic inositol phosphates, which have not been investigated so far in SCLC cells, but have been recently implicated in cell proliferation. Further, different isozymes of phospholipase C are capable of generating varying amounts of cyclic and non-cyclic inositol phosphates. We will determine whether the same or different isozymes of phospholipase C are activated following BB receptor stimulation by different agonists. Cyclic and non-cyclic inositol phosphates generated from inositol labeled tissue following agonist stimulation will be separated by HPLC and quantified. Determinations of cyclic and non-- cyclic inositol triphosphates will be carried out by radioreceptor assay. This will be followed by studies in which cyclic inositol phosphate levels will be altered by modifying the level of phospholipase C or cyclic inositol phosphate hydrolase by the use of specific antibodies to these enzymes and investigating how those changes effect BB-receptor activated mitogenesis. Successful completion of this study will identify additional targets against which future novel pharmacological agents could be developed to treat SCLC.